Virtual machine migration (VM migration) is known in which a virtual machine running on a server is migrated to another server. For example, a migration source server transfers data (memory data) stored in a memory used by a virtual machine to be migrated, to a migration destination server. The migration destination server starts up the virtual machine after the memory transfer from the migration source server is completed.
A data center consumes an enormous amount of electric power because a large number of servers are operated in the data center. Therefore, in the data center, a running virtual machine is migrated so that a server on which no virtual machine is running is made and shut down. Thus, electric power in the data center is saved.
In the course of VM migration, the virtual machine to be migrated is shut down and restarted in another server after a few seconds to a few tens of seconds. During the few seconds, for which the virtual machine is not running, packets to be received by the virtual machine are discarded. Therefore, a virtual machine that provides service in which the packet discard is not allowed may not be migrated freely. Thus, it is difficult to achieve saving of the electric power or perform the maintenance in a server that runs such a virtual machine.
As a technology by which the packet discard is suppressed, VM migration using a migration buffer is known. For example, a migration source server uses the migration buffer to perform the VM migration, and receives a packet destined for a virtual machine to be migrated, into the migration buffer. When memory transfer of the virtual machine is completed and the virtual machine is restarted in a migration destination server, the migration source server transfers the packets stored in the migration buffer to the migration destination server.
Related techniques are disclosed, for example, in International Publication Pamphlet No. WO2010/123140, Japanese Laid-open Patent Publication No. 2012-88863, Japanese Laid-open Patent Publication No. 2011-210032, and Japanese Laid-open Patent Publication No. 2010-257209.
However, in the above-described technology, when an amount of packets stored in the migration buffer is large, or when the communication speed between the servers is slow, the transfer time of the packets becomes long. Therefore, the migrated virtual machine is not allowed to start processing related to packets until the packet transfer is completed. That is, the packet processing by the migrated virtual machine is delayed.